This invention pertains to a method for producing crack-free coatings from a hydrogen silsesquioxane resin on a substrate, preferably a semiconductor substrate. The coatings have a thickness of greater than 1.25 .mu.m and are useful as interlevel dielectrics in the manufacture of semiconductor devices.
The use of hydrogen silsesquioxane resins in the formation of interlevel dielectrics and passivation coatings in the manufacture of semiconductor devices is known in the art. Under the current application method the hydrogen silsesquioxane resin is spun onto the semiconductor device, and any solvent is removed to produce a hydrogen silsesquioxane film on the device. The hydrogen silsesquioxane film is heated by placing the semiconductor device on hot plates (150.degree. C. to 350.degree. C.) to soften and flow the hydrogen silsesquioxane resin and finally the hydrogen silsesquioxane film is cured by heating in an oven at about 400.degree. C. to 450.degree. C. for 1 hour. However, under current application methods, a thin layer (&lt;1.2 .mu.m) of hydrogen silsesquioxane resin ceramic is produced. The thin layers do not adequately cover the metal layer and therefore it is required to apply over the hydrogen silsesquioxane resin ceramic a thick CVD SiO.sub.2 layer to produce the interlevel dielectric.
U.S. Pat. No. 4,756,977 to Haluska et al. discloses the use of hydrogen silsesquioxane resin in the production of mono- or multi-layer coatings on integrated circuits. According to '977 a solvent solution of hydrogen silsesquioxane resin is applied to the device, the solvent is removed and the coating is ceramified by heating to a temperature of between 150 and 1000.degree. C. The mono-layer coatings produced by the method described in '977 have a thickness of approximately 3,000 to 5,000 angstroms (0.3 to 0.5 .mu.m).
Various other methods for curing hydrogen silsesquioxane resin are also known in the art. However, these methods all result in thin (&lt;1.25 .mu.m) coatings. For example, U.S. Pat. Nos. 5,380,567, 5,370,904 and 5,370,903 describe curing of hydrogen silsesquioxane resin in an inert atmosphere. U.S. Pat. No. 5,380,567 to Haluska et al. discloses the cure of hydrogen silsesquioxane resin in an inert atmosphere at temperatures of 500.degree. C. to 1000.degree. C. (coating thickness 0.2 .mu.m). U.S. Pat. No. 5,370,904 to Mine et al. discloses a method for the formation of thick silicon oxide films wherein the method comprises forming a hydrogen silsesquioxane resin film on the surface and thereafter heating the film in an inert atmosphere at a temperature of from 250.degree. C. to 500.degree. C. until the content of the SiH in the silicon oxide product has reached .ltoreq.80% of the content of SiH in the hydrogen silsesquioxane (coating thickness 1.0-1.23 .mu.m). U.S. Pat. No. 5,370,903 to Mine et al. discloses a method for the formation of thick silicon oxide films wherein the method comprises forming a hydrogen silsesquioxane resin film on the surface and thereafter heating the film in a mixed gas atmosphere (.ltoreq.20% vol. O.sub.2) at a temperature of from 250.degree. C. to 500.degree. C. until the content of the SiH in the silicon oxide product has reached .ltoreq.80% of the content of SiH in the hydrogen silsesquioxane (coating thickness 1.02-1.10 .mu.m).
Additionally, U.S. Pat. No. 5,059,448 to Chandra et al. discloses the use of rapid thermal processing to produce coatings of 1 .mu.m or less (0.13 to 0.945 .mu.m). In '448 the hydrogen silsesquioxane resin film is exposed to a high intensity radiation to quickly heat the film at a temperature of 50.degree. C. to 1000.degree. C.
Thicker coatings have been produced by adding fillers to hydrogen silsesquioxane resin. However, because of the presence of the filler and the effect of the filler on the properties of the coating, these coatings are not necessarily suitable as interlevel dielectrics. For Example, U.S. Pat. No. 5,458,912 to Camilletti et al. discloses a method for forming tamper-proof coatings on electronic devices by applying to the device a coating comprising a silica precursor and a filler and thereafter heating at a temperature sufficient to convert the silica precursor to a silica containing ceramic matrix. The coatings produced have thicknesses of 20 to 48 .mu.m.
It is desirable to have thicker coatings produced from hydrogen silsesquioxane to adequately cover the metallization. However, when thick coatings are produced using the current processing methods, they contain undesirable cracks.
It has now been found that when the cure conditions (time, temperature and environment) are controlled, a crack-free insoluble coating having a thickness of greater than 1.25 .mu.m can be produced from hydrogen silsesquioxane resins. These thick coatings have properties equal to or better than the thin coatings produced in the prior art and are suitable as interlevel dielectrics.